Filter medium

ABSTRACT

The present invention relates to a method for the manufacture of a multilayered filter medium whose air permeability is at least 500 l/m 2 sec and a multilayered filter medium obtainable by said method which, when charged with 5 mg/cm 2  SAE-dust of the class “fine”, exhibits a pressure increase of no more than 100 Pa.

The present invention relates to a filter made of a multilayered filtermedium, a method for the manufacture thereof and the use of the filteraccording to the invention.

The use of filters, particularly of multilayered filter media, has longbeen known in the art. For example air filters have long been used inthe automotive sector, in air conditioning systems, indoor filters,pollen filters, clean-room filters, domestic filters etc. Filters havealso long been used for the filtration of fluid media. Examples includeoil filters and hydraulic filters.

Depending upon of the area of application the filters are adapted inorder to achieve a sufficient filtration efficiency and service life.Thus LEFs (Low Efficiency Filters) are used as pre-filters in air/gasand fluid filtration, while High Efficiency Filters are also used in thearea of HEPA (air) or water treatment.

U.S. Pat. No. 5,993,501 discloses multilayered filter media and filtersconsisting of a rigid pleatable base layer, the actual filter layer anda top layer.

EP-A-0980700 discloses filter media and filters with a gradientstructure.

EP-A-0729375 discloses voluminous filter media and filters based oncrimped fibres.

EP-A-0789612 discloses compressed filter media and filters based on meltpolymers.

EP-A-1313538 discloses voluminous filter media and filters based oncrimped fibres and additional microfibres.

EP-A-1378283 also discloses in a general manner multilayered filtermedia and filters.

The aforementioned known filters and filter media are alreadywell-suited for gas and fluid filtration. There is nevertheless a needfor further-improved filters which permit in particular a higher airflow rate and at the same time exhibit a high separation efficiencywithout an excessive pressure loss being observed.

It has been found in a surprising manner that the known filter media canbe significantly improved by the use of special multilayered filtermedia.

The subject-matter of the present invention is therefore a method forthe manufacture of a multilayered filter medium whose air permeabilityis at least 500 l/m²sec comprising the measures:

-   a) Formation of a textile fabric comprising carrier and melt binder    fibres wherein the carrier fibres consist of a polyester and the    melt binder fibres consist of a polymer whose melting point is at    least 5° C. below the melting point of the carrier fibres and the    carrier and melt binder fibres have a titre in the region of 1 to 2    dtex,-   b) Formation of a further textile fabric on the textile surface    formed in step a) comprising carrier and melt binder fibres wherein    the carrier fibres consist of a polyester and the melt binder fibres    consist of a polymer whose melting point is at least 5° C. below the    melting point of the carrier fibres and the carrier and melt binder    fibres have a titre in the region of 2 to 4 dtex,-   c) Formation of a further textile fabric on the textile surface    formed in step b) comprising carrier and melt binder fibres wherein    the carrier fibres consist of a polyester and the melt binder fibres    consist of a polymer whose melting point is at least 5° C. below the    melting point of the carrier fibres and the carrier and melt binder    fibres have a titre in the region of 4 to 12 dtex,-   d) The portion of the textile fabric formed in step a) is 20 to 60%    by weight, the portion of the textile fabric formed in step b) is 10    to 40% by weight and the portion of the textile fabric formed in    step c) is 10 to 40% by weight,-   e) The portion of the melt binder fibres in the textile fabric    formed in accordance with steps a) to c) is 5 to 40% by weight,-   f) The weight per unit area of the textile fabric formed in    accordance with steps a) to c) is 50 to 400 g/m²,-   g) Pre-solidification of the multilayered textile fabric formed in    accordance with steps a) to c) by means of a heated roller whose    surface temperature is at least 70° C.,-   h) Calendering of the pre-solidified multilayered textile fabric    formed in accordance with step g) by means of a calender whose    surface temperature is at least 10° C. below the melting temperature    of the melt binder fibres and a contact pressure/line pressure of at    least 20 daN,-   i) Introduction of the multilayered textile fabric calendered in    accordance with step h) into a hot-air oven whose minimum    temperature is equal to or above the melting temperature of the melt    binder fibres and whose maximum temperature is at least 10° C. below    the melting temperature of the carrier fibres wherein the introduced    textile fabric expands and the thickness of the textile fabric    increases by at least 30% with respect to the introduced textile    fabric,-   j) Cooling of the melt binder-solidified multilayered filter medium    and assembly.

A further subject-matter of the present invention is a method for themanufacture of a multilayered filter medium comprising the measures a)to j), wherein, as a further measure c′), at least one further textilefabric comprising carrier and melt binder fibres, preferably bicomponentfibres, particularly of the core-sheath type is formed on the textilesurface formed in step c), wherein the carrier fibres consist of apolyester and the melt binder fibres consist of a polymer whose meltingpoint is at least 5° C. below the melting point of the carrier fibresand the carrier and melt binder fibres have different titres in theregion of 1 to 12 dtex, wherein the further textile fabric(s) has aweight per unit area of 50-400 g/m², preferably 50-200 g/m² and theportion of the melt binder fibres in the further textile fabric is 5 to40% by weight.

The formation of the textile fabrics in step a) to c) and/or c′) iscarried out using known methods. The textile fabrics formed inaccordance with the invention concern pleatable nonwoven fabrics,preferably staple fibre nonwoven fabrics and/or spunbonded nonwovenfabrics, particularly spunbonded nonwoven fabrics. Spunbonded nonwovenfabrics, i.e. so-called spunbonds, are produced by a random depositionof freshly melt-spun filaments. The filaments are endless syntheticfibres made of melt-spinnable polymer materials.

The textile fabrics formed in accordance with the invention,particularly the formed nonwoven fabrics, have no texturing, i.e.crimping.

The carrier fibres preferably comprise and/or consist of the spunbondednonwoven fabrics made of melt-spinnable polyesters. In principle, allsuitable known polyester material types may be considered with respectto fibre manufacture. Such polyesters predominantly consist of modulesderiving from aromatic dicarboxylic acids and of aliphatic diols. Commonaromatic dicarboxylic acid modules are the bivalent residues of benzenedicarboxylic acids, particularly of terephthalic acid and isophthalicacid; common diols have 2 to 4 C-atoms, wherein the ethylene glycol isparticularly suitable. Particularly advantageous are spunbonded nonwovenfabrics, which consist up to at least 85 mol % of polyethyleneterephthalate. The remaining 15 mol % then comprise dicarboxylic acidunits and glycol units which act as so-called modification agents andwhich permit the specialist in the art to influence the physical andchemical properties of the manufactured filaments in a targeted manner.Examples of such dicarboxylic acid units are residues of isophthalicacid or of aliphatic dicarboxylic acid such as e.g. glutaric acid,adipic acid, sebacic acid; examples for diol residues with modifyingaction are those of long chained diols, e.g. of propane diol or butanediol, of di- or triethylene glycol or, if available in small quantities,of polyglycol with a molar weight of approx. 500 to 2000.

Particularly preferred are carrier fibres made of polyester, whichcontain at least 95 mol % polyethylene terephthalate (PET), particularlythose made of unmodified PET.

The polyesters used in accordance with the invention preferably have amolecular weight corresponding to an intrinsic viscosity (IV), measuredin a solution of 1 g polymer in 100 ml dichloroacetic acid at 25° C., of0.6 to 1.4.

As hot-melt adhesive fibres particularly polymers and/or modifiedpolyesters having a melting point which is 10 to 50° C., preferably 30to 50° C., lower with respect to the carrier fibre raw material may beconsidered. Examples of a such holt-melt adhesives are polypropylene,polybutene terephthalate or condensation of long-chain diols and/orpolyethylene terephthalate modified by isophthalic acid or aliphaticdicarboxylic acids.

Carrier and hot-melt adhesive fibres are preferably based on a polymerclass. This means that all employed fibres from a substance class areselected such that these can be recycled without difficulty after use ofthe nonwoven fibre. Should the carrier fibres consist for example ofpolyester, the holt-melt adhesive fibres are also selected for examplefrom polyesters or from a mixture of polyesters, e.g. as bicomponentfibres with PET in the core and a low temperature-melting polyethyleneterephthalate copolymer as a sheath. Furthermore bicomponent fibresbased on different polymers are, however, also possible.

Such melt binder-solidified spunbonded nonwoven fabrics are described indetail for example in EP-A-0,446,822 and EP-A-0,590,629.

The hot melt adhesives are introduced to the nonwoven fabric in fibreform. In this case it is beneficial to co-extrude the hot-melt fibreswith the carrier fibres such that a homogenous distribution of the twofibre types is achieved.

The filaments or staple fibres on which the nonwoven fabrics are basedmay have a practically round cross section or may also have other shapessuch as dumbbell, oval, triangular and/or trilobal or multilobal crosssections. Hollow fibres and bicomponent or multicomponent fibres canalso be used. Furthermore, the hot-melt adhesive fibres can also be usedin the form of bicomponent or multicomponent fibres.

In a further embodiment of the invention bicomponent or multicomponentfibres can also be used instead of the carrier and melt binder fibres.This preferably concerns so-called core-sheath bicomponent fibres,wherein these can also be formed eccentrically. This hereby also permitsa particularly homogenous distribution of the two types.

If bicomponent fibres of the core-sheath type are used in place of thecarrier and melt binder fibres the core is formed from the same materialas the previously-cited carrier fibres and the sheath from the samematerial as the previously-cited melt binder fibres. The melting pointof the sheath component is preferably at least 5° C. below the meltingpoint of the core components, preferably at least 10° C. below themelting point of the core components.

The fibres forming the nonwoven fabric can be modified by the usualadditives, for example by antistatic agents such as carbon black oradditives which permit electrostatic charging. Furthermore additives forimproving the flame resistance are possible.

The weight per unit area of the textile fabric formed in accordance withthe steps a) to c) is between 50 and 400 g/m², preferably 100 and 350g/m², particularly 150 and 300 g/m².

In so far as the multilayered filter medium according to the inventionrequires further solidification, this is carried out by needling,particularly hydrodynamically.

In a preferred embodiment the multilayered filter medium according tothe invention is solidified exclusively with thermoplastic binderswithout needling and without the addition of chemical binders.

In a preferred embodiment of the invention, the portion of the textilefabric formed in step a) is 30 to 50% by weight of the textile fabricformed in accordance with the steps a) to c).

In a preferred embodiment of the invention the portion of the textilefabric formed in step b) is 20 to 30% by weight of the textile fabricformed in accordance with the steps a) to c).

In a preferred embodiment of the invention the portion of the textilefabric formed in step c) is 20 to 30% by weight of the textile fabricformed in accordance with the steps a) to c).

Particularly preferably, the portion of the textile fabric formed instep a) is 30 to 50% by weight, the portion of the textile fabric formedin step b) is 20 to 30% by weight and the portion of the textile fabricformed in step c) is 20 to 30% by weight with respect to the textilefabric formed in accordance with the steps a) to c).

In a preferred embodiment of the invention the portion of the meltbinder fibres in the textile fabric formed in accordance with the stepsa) to c) is 10 to 40% by weight.

In a preferred embodiment of the invention the previously describedmulticomponent and/or bicomponent fibres are wholly or partly usedinstead of the carrier and melt binder fibres. By using suchmulticomponent and/or bicomponent fibres the portion of melt binder canalso be reduced such that said melt binder in the case of the textilefabric formed in accordance with the steps a) to c) is 10 to 30% byweight.

The pre-solidification of the multilayered textile fabric formed inaccordance with the steps a) to c) and/or a) to c′) takes place by meansof one or more consecutively arranged, heated cylinders whose surfacetemperature is at least 70° C. Particularly preferably thepre-solidification takes place without additional contact pressure. Thesurface temperature is preferably at least 100° C. The surfacetemperature is preferably at least 10° C. below the melting temperatureof the melt binder fibres, particularly at least 30° C. below themelting temperature of the melt binder fibres. Particularly preferablythe pre-solidification takes place at a temperature and/or surfacetemperature of the rollers which is below the calendering temperature.

The calendering of the multilayered textile fabric pre-solidified inaccordance with step g) preferably takes place by means of a calenderwhose surface temperature is at least 15° C. below the meltingtemperature of the melt binder fibres, particularly at least 20° C.below the melting temperature of the melt binder fibres.

The calendering of the multilayered textile fabric pre-solidified inaccordance with step g) preferably takes place by means of a calenderand a contact pressure/line pressure of at least 20 daN, particularly of40 to 60 daN.

The calendering of the multilayered textile fabric pre-solidified inaccordance with step g) preferably takes place at the aforementionedcontact pressure/line pressure and aforementioned surface temperature.

After the calendering in accordance with step h), the calenderedmultilayered textile fabric is introduced into a hot-air oven. Thetemperature of the hot air blown into the hot-air oven is at least atthe melting temperature of the melt binder fibres (lower limit) and atleast 10° C. below the melting temperature of the carrier fibres (upperlimit). The hot-air ovens employed in accordance with the invention areknown to the person skilled in the art. Said hot-air ovens may have onemore drums. In so far as the hot-air ovens have several drums, forexample three drums, the textile fabric is guided alternately around thelower and/or upper half of the drum. The hot air is generated centrallyand sucked through the textile fabric and/or nonwoven fabric and theperforated drum into the interior of the drums. Such hot-air ovens areobtainable from the company Fleissner as so-called through-air dryers.

The textile fabric and/or nonwoven fabric is preferably guided at aspeed of 10 m/min (±20%, particularly preferably ±10%) through the oven.

The dwell time of the textile fabric and/or nonwoven fabric in the ovenis preferably 20 sec (±20%, particularly preferably ±10%).

By means of the special combination of special individual layers inaccordance with the steps a) to c) and/or a) to c′) and theircomposition in accordance with step d) in combination with thecombination of pre-solidification in accordance with step g) andcalendering in accordance with step h) a textile fabric, particularly anonwoven fabric, is produced which can expand in the case ofthermoplastic solidification in the hot-air oven. In this case thethickness increases by at least 30%, preferably by at least 35%,particularly by at least 40%, each with respect to the textile fabricand/or nonwoven fabric introduced into the hot-air oven.

Due to the expansion described above, the air permeability of themultilayered filter medium increases by more than 50%, preferably bymore than 80%, each with respect to the textile fabric and/or nonwovenfabric introduced into the hot-air oven.

The air permeability of the multilayered filter medium manufactured inaccordance with the invention is at least 500 l/m²sec, measuredaccording to ISO 9237.

The multilayered filter media manufactured by means of the method inaccordance with the invention is distinguished by particularly goodfiltration characteristics, particularly in the case of SAE dusts of theclass “fine” (ISO Fine).

Thus a multilayered filter medium manufactured using the method inaccordance with the invention having a weight per unit area of 180 g/m²,when charged with 5 mg/cm² SAE dust of the class “fine”, exhibits apressure increase of no more than 70 Pa. The measurement of the pressureincrease and charging is carried out with a PALAS dust generator andmeasuring device MFP 2000 from the company PALAS.

A further subject-matter of the present invention is thus a multilayeredfilter medium, whose air permeability is at least 500 l/m²sec and whichhas at least three concrete layers, wherein

-   I) the first layer is a melt binder-solidified textile fabric whose    fibres have a titre in the range of 1 to 2 dtex,-   II) the second layer is a melt binder-solidified textile fabric    whose fibres have a titre in the range of 2 to 4 dtex,-   III) the third layer is a melt binder-solidified textile fabric    whose fibres have a titre in the range of 4 to 12 dtex,-   IV) the portion of the first layer of the multilayered filter medium    is 20 to 60% by weight, the portion of the second layer of the    multilayered filter medium is 10 to 40% by weight and the portion of    the third layer of the multilayered filter medium is 10 to 40% by    weight,-   V) the melt binder portion in the layers in accordance with I)    to III) amounts to 5 to 40% by weight in total,-   VI) the weight per unit area of the layers in accordance with I)    to III) amounts to 50 to 400 g/m² in total and-   VII) the filter medium, when charged with 5 mg/cm² SAE dust of the    class “fine”, has a pressure increase of no more than 100 Pa,    preferably of no more than 70 Pa.

A further subject-matter of the present invention is thus a multilayeredfilter medium whose air permeability is at least 500 l/m²sec and whichhas at least three concrete layers, wherein

-   I) the first layer is a melt binder-solidified textile fabric whose    fibres have a titre in the range of 1 to 2 dtex,-   II) the second layer is a melt binder-solidified textile fabric    whose fibres have a titre in the range of 2 to 4 dtex,-   III) the third layer is a melt binder-solidified textile fabric    whose fibres have a titre in the range of 4 to 12 dtex,-   IV) the fourth layer is a melt binder-solidified textile fabric    whose fibres have different titres in the range of 1 to 12 dtex and    a weight per unit area of 50-400 g/m², preferably a weight per unit    area of 50-200 g/m²,-   V) the portion of the first layer of the multilayered filter medium    in accordance with I) to III) is 20 to 60% by weight, the portion of    the second layer of the multilayered filter medium in accordance    with I) to III) is 10 to 40% by weight and the portion of the third    layer of the multilayered filter medium in accordance with I)    to III) is 10 to 40% by weight,-   VI) the melt binder portion in the layers in accordance with I)    to IV) amounts to 5 to 40% by weight in total,-   VII) the weight per unit area of the layers in accordance with I)    to III) amounts to 50 to 400 g/m² in total and    the filter medium, when charged with 5 mg/cm² SAE dust of the class    “fine”, exhibits a pressure increase of no more than 100 Pa,    preferably of no more than 70 Pa.

The melt binder-solidified textile fabrics in accordance with I) to III)and/or I) to IV) can from be formed from the above-described carrier andmelt binder fibres or by the above-described multicomponent and/orbicomponent fibres. The preferred embodiments specified in connectionwith the method also apply for the multilayered filter medium accordingto the invention.

The multilayered filter medium according to the invention may exhibitadditional supporting nonwoven fabric layers and/or top layers. Suchadditional layers are known, for example, from DE102007027299.

The multilayered filter medium according to the invention can beadditionally equipped with functional materials. For example coatingswith conductive or antibacterial materials may also be executed. Thismakes it possible to adapt the characteristics profile of the filtermedium to special requirements.

The filter media according to the invention are used in air/gas andfluid filtration, particularly in the automotive sector, in airconditioning systems, indoor area filters, pollen filters, clean-roomfilters, domestic filters and as oil filters and hydraulic filters.

Filter elements and filter bags as well as filter modules and/orcartridges containing the filters according to the invention aretherefore also subject-matter of the present invention. In this case thefilters may be installed in housings or other casings in pleated form.Corresponding embodiments are disclosed by U.S. Pat. No. 5,883,501.

A further area of application of the filters according to the inventionis so-called LEF (Low Efficiency Filters) and HEPA (High EfficiencyParticulate (Air) Filters) wherein the latter can also be used in watertreatment. In accordance with EN 1822, the HEPA filters are alsodesignated as filter classes H10 to H14.

A further area of application of the filters according to the inventionare so-called HVAC and so-called ASHRAE filter media.

A further area of application of the filters according to the inventionare so-called ULPA filters, i.e. for clean and ultraclean rooms (ISOclass 1000 and better). In accordance with EN 1822, ULPA filters arealso designated as filter classes U15 to U17.

The following examples serve to explain the invention without limitingthe invention.

EXAMPLE 1

A filter medium has been manufactured with the aid of the spunbondmethod. In this case PET filament layers of 1.7 dtex, 3.4 dtex and 6.2dtex each having two spin beams were produced and laid on the foldingbelt. The following process parameters were set in this case:

Weight per unit area: approx. 180 g/m²Hot roller: 100° C.Calender: 160° C., 24 daN/cm²Oven: 235° C. (Fleissner rotary drum drier)Line speed: 6.6 m/min

The testing of the filter medium according to the invention (047/180)shows in comparison (FIG. 1) with a conventionally manufactured filtermedium (478/170) having a comparable weight per unit area that themultilayered filter medium manufactured using the method in accordancewith the invention, when charged with 5 mg/cm² SAE dust of the class“fine”, exhibits a pressure increase of no more than 70 Pa whereas aconventionally manufactured filter medium exhibits the significantlyhigher pressure increase of 1800 Pa.

The filter charge was determined and the consequential pressure increasewas measured with the help of the PALAS MFP 2000 dust generator. Themeasurement was carried out on a 100 cm² sample at a flow speed of 20cm/sec at a dust concentration in the air of 200 mg/m³.

EXAMPLE 2

In order to determine the air permeability a filter element wasmanufactured in accordance with example 1, however with a weight perunit area of approx. 250 g/m². In this case the thickness of thenonwoven fabric and the air permeability were measured before (SampleX01) and after (Sample X02) calendering. The results are shown in Table1.

TABLE 1 Weight Thickness Increase in Air Air Sample g/m² mm thickness %l/m²s increase % V09027[01] 247 1.10 317 V09027[02] 252 1.56 42 705 122

1. A method for the manufacture of a multilayered filter medium whoseair permeability is at least 500 l/m²sec comprising the measures: a)Formation of a textile fabric comprising carrier and melt binder fibreswherein the carrier fibres consist of a polyester and the melt binderfibres consist of a polymer whose melting point is at least 5° C. belowthe melting point of the carrier fibres and the carrier and melt binderfibres have a titre in the region of 1 to 2 dtex, b) Formation of afurther textile fabric on the textile surface formed in step a)comprising carrier and melt binder fibres wherein the carrier fibresconsist of a polyester and the melt binder fibres consist of a polymerwhose melting point is at least 5° C. below the melting point of thecarrier fibres and the carrier and melt binder fibres have a titre inthe region of 2 to 4 dtex, c) Formation of a further textile fabric onthe textile surface formed in step b) comprising carrier and melt binderfibres wherein the carrier fibres consist of a polyester and the meltbinder fibres consist of a polymer whose melting point is at least 5° C.below the melting point of the carrier fibres and the carrier and meltbinder fibres have a titre in the region of 4 to 12 dtex, d) The portionof the textile fabric formed in step a) is 20 to 60% by weight, theportion of the textile fabric formed in step b) is 10 to 40% by weightand the portion of the textile fabric formed in step c) is 10 to 40% byweight, e) The portion of the melt binder fibres in textile fabricformed in accordance with steps a) to c) is 5 to 40% by weight, f) Theweight per unit area of the textile fabric formed in accordance withsteps a) to c) is 50 to 400 g/m², g) Pre-solidification of themultilayered textile fabric formed in accordance with steps a) to c) bymeans of a heated roller whose surface temperature is at least 70° C.,h) Calendering of the pre-solidified multilayered textile fabric formedin accordance with step g) by means of a calender whose surfacetemperature is at least 10° C. below the melting temperature of the meltbinder fibres and a contact pressure/line pressure of at least 20 daN.i) Introduction of the multilayered textile fabric calendered inaccordance with step h) into a hot-air oven whose minimum temperature isequal to or above the melting temperature of the melt binder fibres andwhose maximum temperature is at least 10° C. below the meltingtemperature of the carrier fibres wherein the introduced textile fabricexpands and the thickness of the textile fabric increases by at least30% with respect to the introduced textile fabric, j) Cooling of themelt binder-solidified multilayered filter medium and assembly.
 2. Themethod according to claim 1, characterized in that further textilefabrics are formed after step f) and before step g).
 3. The methodaccording to claim 1 or 2, characterized in that the textile fabricsformed according to steps a) to c), and any possible formed furthertextile fabrics concern nonwoven fabrics, preferably staple fibrenonwoven fabrics and/or spunbonded nonwoven fabrics.
 4. The methodaccording to claim 1, 2 or 3, characterized in that the carrier and meltbinder fibres are co-extruded.
 5. The method according to claims 1 to 3,characterized in that instead of the carrier and melt binder fibresbicomponent fibres of the core-sheath type are used whose core is formedfrom polyester and whose sheath is formed from a polymer whose meltingpoint is at least 5° C. below the melting point of the core component,preferably at least 10° C. below the melting point of the corecomponent.
 6. The method according to one or more of the claims 1 to 5,characterized in that the weight per unit area of the textile fabricformed in accordance with the steps a) to c) is 50 to 350 g/m²,preferably 50 to 300 g/m².
 7. The method according to one or more of theclaims 1 to 6, characterized in that the pre-solidification of themultilayered textile fabric formed in accordance with the steps a) to c)takes place by means of a heated roller whose surface temperature is atleast 70° C., preferably without additional contact pressure, preferablyat a surface temperature of at least 100° C.
 8. The method according toone or more of the claims 1 to 6, characterized in that thepre-solidification of the multilayered textile fabric formed inaccordance with the steps a) to c) takes place at a maximum surfacetemperature of at least 10° C. below the melting temperature of the meltbinder fibres, particularly at least 30° C. below the meltingtemperature of the melt binder fibres.
 9. The method according to one ormore of the claims 1 to 8, characterized in that the calendering of themultilayered textile fabric pre-solidified in accordance with step g)takes place by means of calenders whose surface temperature is at least15° C. below the melting temperature of the melt binder fibres and/ormelt binder components, preferably at least 20° C. below the meltingtemperature of the melt binder fibres and/or melt binder component. 10.The method according to one or more of the claims 1 to 9, characterizedin that the calendering of the multilayered textile fabricpre-solidified in accordance with step g) takes place by means ofcalenders and a contact pressure/line pressure of at least 20 daN,preferably of 40 to 60 daN.
 11. The method according to one or more ofthe claims 1 to 8, characterized in that after the calendering inaccordance with step h) the calendered multilayered textile fabric isintroduced into a hot-air oven.
 12. The method according to claim 11,characterized in that the temperature of the hot air blown into thehot-air oven is the same as or above the melting temperature of the meltbinder fibres and/or melt binder component and at least 10° C. below themelting temperature of the carrier fibres and/or core component.
 13. Themethod according to claim 11 or 12, characterized in that the hot air issucked through the textile fabric and/or nonwoven fabric and theperforated drum in the interior of the hot-air oven.
 14. The methodaccording to claim 11, 12 or 13, characterized in that the textilefabric and/or nonwoven fabric is guided through the hot-air oven at aspeed of 10 m/sec (±20%).
 15. The method according to one or more of theclaims 11 to 14, characterized in that the dwell time of the textilefabric and/or nonwoven fabric in the hot-air oven is 20 secs (±20%). 16.The method according to one or more of the claims 1 to 15, characterizedin that the thickness of the textile fabric increases during thethermoplastic solidification in the hot-air oven by at least 35%,preferably by at least 40%, each with respect to the textile fabricintroduced into the hot-air oven.
 17. The method according to one ormore of the claims 1 to 15, characterized in that the fibres of thetextile fabric and/or nonwoven fabric formed have no texturing.
 18. Amultilayered filter medium whose air permeability is at least 500l/m²sec and which has a least three concrete layers, wherein I) thefirst layer is a melt binder-solidified textile fabric whose fibres havea titre in the range of 1 to 2 dtex, II) the second layer is a meltbinder-solidified textile fabric whose fibres have a titre in the rangeof 2 to 4 dtex, III) the third layer is a melt binder-solidified textilefabric whose fibres have a titre in the range of 4 to 12 dtex, IV) theportion of the first layer of the multilayered filter medium is 20 to60% by weight, the portion of the second layer of the multilayeredfilter medium is 10 to 40% by weight and the portion of the third layerof the multilayered filter medium is 10 to 40% by weight, V) the meltbinder portion in the layers in accordance with I) to III) amounts to 5to 40% by weight in total, VI) the weight per unit area of the layers inaccordance with I) to III) amounts to 50 to 400 g/m² in total and VII)the filter medium, when charged with 5 mg/cm³ SAE dust of the class“fine”, exhibits a pressure increase of no more than 100 Pa.
 19. Thefilter medium according to claim 18, characterized in that the meltbinder-solidified textile fabrics in accordance with I) to III) areformed from the carrier and melt binder fibres or from multicomponentand/or bicomponent fibres, particularly of the core-sheath type.
 20. Thefilter medium according to claim 18 or 19, characterized in that thefilter medium, when charged with 5 mg/cm³ SAE dust of the class “fine”,exhibits a pressure increase of no more than 70 Pa.
 21. The filtermedium according to one or more of the claims 18 to 20, characterized inthat it has additional melt binder-solidified textile fabrics whosefibres have different titres in the range of 1 to 12 dtex and which havea weight per unit area of 50-400 g/m², preferably a weight per unit areaof 50-200 g/m².
 22. The filter medium according to one or more of theclaims 18 to 21, characterized in that the fibres of the formed textilefabrics and/or nonwoven fabrics have no texturing.
 23. The filter mediumaccording to one or more of the claims 18 to 22, characterized in thatit has further supporting nonwoven fabric layers and/or top layers. 24.The filter medium according to one or more of the claims 18 to 23,characterized in that it is pleatable.
 25. The use of the filter mediadefined in the claims 18 to 24 in air/gas and fluid filtration. 26.Filter modules containing a housing and at least one filter defined inthe claims 18 to 24.